Which of the following is diamagnetic in nature ?

Options

A. `Co^(3+)`, octahedral complex with weak field ligands
B. `Co^(3+)`, octahedral complex with strong field ligand
C. `Co^(2+)` in tetrahedral complex
D. `Co^(2+)` in square planar complex

Answer

B

Explanation

`._(27)Co=3d^(7)4s^(2),Co^(3+)=3d^(6)4s^(0)`

In a strong field ligand, electrons pair up. Hence, it is diamagnetic in nature.